A boat carrying about 40 migrants sank off the coast of Mauritania, leaving one survivor, the U.N. refugee agency said Thursday.
The U.N. says the sole survivor is from Guinea and that the others on board were also from sub-Saharan African countries.
The vessel was apparently heading for the Canary Islands.
"These are the awful consequences of immoral and unscrupulous smugglers and traffickers arranging these desperate sea journeys," U.N. Refugee Agency spokesman Charlie Yaxley tweeted.
The Spanish interior ministry says about 2,800 illegal migrants arrived on the Canary Islands between January and July - five times as many as during the same period last year.
The migrants are looking to escape poverty and war in Africa and for the chance of a better life in the European Union.
More than 60 migrants died and 80 others desperately swam to shore when a refugee-packed boat from Gambia sank off the Mauritanian coast in December.